1. Field of the Invention
The present invention relates to a travel detecting apparatus for detecting travel variations of a vehicle such as a motor vehicle in accordance with pulses generated in response to the travel of the vehicle.
2. Description of the Prior Art
A conventional travel detecting apparatus is constructed so that pulse signals are generated by a sensor connected to an automotive transmission. A cycle (frequency) of the pulse signals is varied in response to the rotation of the transmission, so that the number of revolutions per minute (RPM) or travelled distance may be detected by the measurement of the cycle of the pulse signals.
In the conventional travel detecting apparatus, even if the pulse signals of the same cycle would be produced exactly in accordance with RPM of the transmission, there would be errors in accordance with a diameter of tires which would be changed, so that the indicated travelled distance would be different from the actual travelled distance or an indicated speed of the vehicle would be different from the actual speed. For this reason, it is necessary to provide a speedometer or an odometer (travel meter) in accordance with the diameter of the tires. In order to commonly use indicators such as a speedometer or an odometer for different tire diameters, it is necessary to change a coupling gear ratio of a sensor relative to the transmission. In any case, to meet these requirements, it is necessary to increase the number of the mechanical or electric parts.